As a known technology, a magnetic sensor which detects a rotation angle of an object using a GMR element (Giant Magneto Resistance; GMR), or a TMR element (Tunneling Magneto Resistance; TMR), which has a free magnetic layer and a pin magnetic layer, is known. With these elements, an angle can be detected by the output of the element varying in accordance with a difference between the magnetization direction of the pin magnetic layer fixed in one direction and the magnetization direction of the free magnetic layer influenced by an external magnetic field.
Normally, the magnetization direction of the pin magnetic layer is determined by carrying out annealing at in the order of 300° while applying a magnetic field. In this case, as the magnetization of each pin magnetic layer is carried out while applying a magnetic field to the whole of a wafer on which a plurality of elements are formed, all the magnetization directions of the pin magnetic layers are the same direction in one wafer. Because of this, an output signal is of one of a cosine curve or a sine curve, and 360° cannot be detected using one element.
Hence, in order to enable a detection of 360°, there is a need for a structure wherein a cosine curve and a sine curve can be obtained by disposing two chips so that the magnetization directions of the pin magnetic layers differ 90° from one another. In order to realize this structure, heretofore, a plurality of elements having pin magnetic layers whose magnetization directions are the same have been formed on one wafer, as heretofore described, and after the wafer has been divided into chips, one for each of the elements, two chips have been packaged so that the magnetization directions of the pin magnetic layers differ 90° from one another.
However, with this method, as the number of chips increases, there has been a problem in that the method leads to an increase in cost. Also, as it is necessary to control the directions of the chips so that the magnetization directions of the pin magnetic layers differ 90° from one another, there has been a possibility of rotation detection accuracy decreasing due to an assembly error. Because of this, a pin magnetic layer multipolarization technology wherein a large number of magnetization directions are provided in one wafer is demanded.
Hence, Patent Document 1 proposes a method whereby a magnetic field is applied to a wafer on which a large number of elements are formed, and an element, the magnetization direction of whose pin magnetic layer is intended to be fixed, is irradiated with a current pulse or a laser pulse, thus fixing the pin magnetic layer of the element irradiated with the pulse. With this method, the magnetization direction of each pin magnetic layer can be controlled without dividing the wafer.
However, in Patent Document 1, as the element on the wafer is irradiated with a current pulse or a laser pulse, the heat of the pulse diffuses to the wafer. Because of this, there is a problem in that the accuracy of magnetization of the pin magnetic layer of the element decreases, and thus detection accuracy decreases.
As another technology of heating elements, a technology whereby an action of an MRAM device is aided by the heat of a heater material is proposed in JP-A-2005-150739. However, as it is necessary, when magnetizing a pin magnetic layer, to heat the pin magnetic layer at a temperature of approximately 300° C., the heater material for aiding the action of the MRAM device cannot be used in magnetization.
Also, Patent Document 2 proposes a method of providing a difference in magnetization angle between a heating region and a non-heating region by heating one portion of elements. Specifically, as a method for changing the magnetization directions of elements in the same chip in a reproduction magnetic head, a magnetization angle adjusting method using the fact that a difference in holding power occurs between magnetic bodies when heating one portion of the elements is proposed in Patent Document 2.
As a structure of a magnetic head, Patent Documents 3 and 4 propose a structure wherein a recessed portion is provided in a substrate, an insulating body is formed in the recessed portion, and a coil is formed on the insulating body.
However, with the heating method shown in Patent Document 2, when long time heating is carried out on one portion of the elements in order to carry out sufficient magnetization, thermal diffusion occurs wherein heat conducts through the substrate, and there is a problem in that another element is also overheated. Because of this, an angle error occurs in each element, affecting detection accuracy. Consequently, in a magnetic sensor, of which angle detection accuracy is required, such as detects a rotation angle, a structure is demanded wherein magnetization directions can be changed on one chip while reducing an angle error caused by thermal diffusion.
Patent Document 1: JP-A-2003-502876
Patent Document 2: JP-A-2006-269866
Patent Document 3: JP-A-H9-22510
Patent Document 4: JP-A-H9-22512